Method and device for controlling the stability of a vehicle, in particular a utility vehicle

ABSTRACT

The invention relates to a method and a device for controlling the stability of a vehicle, in particular a utility vehicle, in which an anti-tilt control method is carried out in which at least one lateral acceleration signal (ay), one steering wheel angle signal (LRW) and one vehicle speed signal (v) are sensed and control signals (S 1 , S 2 ) for vehicle interventions are formed therefrom and output, and a yaw control method is carried out during which the steering wheel angle signal (LRW), the lateral acceleration signal (ay) and the vehicle speed signal (v) are sensed, a yaw rate setpoint value signal (ψs) and a yaw rate actual value signal (ψi) are determined and compared with one another and a yaw control process is carried out during which control signals (S 3 , S 4 , S 5 ) for vehicle interventions are formed and output.

The invention generally relates to embodiments of a method and a devicefor controlling the stability of a vehicle, in particular a utilityvehicle.

Stability control systems of vehicles serve to intervene in criticalsituations of the vehicle such as, for example, understeering,oversteering or a tendency to tilt by means of, inter alia, brakinginterventions, in particular modulation of the brake pressure, in such away as to assist the driving of the vehicle.

Input variables which are used in this context are measurement signalsof different sensors, in particular of a yaw rate sensor, steering wheelangle sensor and lateral acceleration sensor as well as, if appropriate,of a longitudinal acceleration sensor; in addition, driving statevariables such as, for example, the mass of a vehicle and a referencespeed, which are determined by other brake control systems such as ABSor EBS systems, are used to a certain extent.

In particular in utility vehicles, stability control systems are usedwhich have one control circuit for yaw control and a further controlcircuit for anti-tilt control. The anti-tilt controller generallyreceives input signals for the lateral acceleration, the vehicle masswhich is determined and the vehicle reference speed and, if appropriate,a steering wheel angle signal. The yaw controller generally receives thesteering wheel angle signal, the vehicle reference speed and the yawrate signal.

The extensive sensor systems result in corresponding costs both for thehardware of the sensors used and for the software implementation.Furthermore, the sensors, in particular the yaw rate sensor, aresusceptible to faults so that a high degree of expenditure on softwaredevelopment is necessary for reliable implementation.

Furthermore, the individual control channels give rise to correspondingcosts for the brake system, the yaw controller in this context requiringtwo individual control channels for the front axle.

An object of the invention is to provide a method and a device forcontrolling the stability of a vehicle which permit reliable control ofthe driving stability with relatively little expenditure.

This object is achieved by means of a method according to claim 1 and adevice according to claim 14. The subclaims describe preferredembodiments.

Inventive embodiments involve estimating the actual yaw behaviour fromthe measured lateral acceleration, and determining the setpoint yawbehaviour from the steering wheel angle signal, and of comparing withone another the actual values and setpoint values of the yaw behaviourwhich are acquired in this way. In contrast to conventional systems,according to the invention no specific yaw rate sensor is needed for yawcontrol in order to output a yaw rate measurement signal.

This is based on the inventive realization that a lateral accelerationsignal is used in any case for anti-tilt control or rolling stabilitycontrol and this lateral acceleration signal can basically also be usedfor limiting the inclination to understeer in the yaw control without anadditional yaw rate signal or yaw rate measurement signal. In contrastto existing anti-tilt controllers, in this context the steering wheelangle sensor is not dispensed with but rather the latter is consciouslyincluded not only in the anti-tilt control but also in the yaw control.As a result, a relatively high level of performance, in particular inthe case of dynamic manoeuvres, is obtained compared to known anti-tiltcontrol systems or rolling stability control systems without a steeringwheel angle sensor.

The method according to embodiments of the invention and the deviceaccording to embodiments of the invention are advantageous in particularin vehicles with a large wheel base, for example lorries and buses,since the latter tend to understeer in the case of instability at lowvalues of the coefficient of friction. In this context, according to theinvention it is realized that in such vehicles an understeeringintervention by braking the rear wheels on the inside of a bend is veryeffective while, in contrast, an oversteering intervention by brakingthe front wheel on the outside of a bend is less effective. In the caseof train systems, the method according to embodiments of the inventionis relevant in particular for the traction vehicle.

The anti-tilt control process can be carried out, in particular, on allwheels of the traction vehicle and trailer vehicle.

By eliminating the yaw rate sensor which is very costly in terms ofhardware and software and is also susceptible to faults, and byincluding the steering wheel angle signal and lateral accelerationsignal, a cost-effective and nevertheless very reliable, robust systemis provided for the anti-tilt control and for the yaw control.

The invention will be explained below with reference to the appendeddrawing of an exemplary embodiment.

FIG. 1 shows a block diagram of a stability control system according toan embodiment of the invention.

In the stability control system 1 shown in FIG. 1, an anti-tilt controlsystem 2 and a yaw control system 3 are provided as two control systemswith common input signals. The control systems 2 and 3 may be embodiedhere in terms of software in a common control unit or in two controlunits which are separated in terms of hardware.

The anti-tilt control system 2 receives as an input signal a vehiclemass signal m which is determined by a subordinate brake system, forexample an ABS or EBS control system, in a manner known per se as areference value from the inertia when different accelerations or brakingeffects are acting, if appropriate including axle load sensors.Furthermore, the anti-tilt control system 2 receives a vehicle speedsignal v which is present, for example, in the brake systems of the ABSor EBS system as a reference speed and is determined, in particular,from the wheel speeds which are determined by wheel speed sensors, andforms the basis of the additionally implemented slip control systemsand, if appropriate, braking force distribution systems. As analternative, a measurement signal can also be received from a wheel axleas a vehicle speed signal v. Furthermore, the anti-tilt control system 2receives a lateral acceleration signal ay from a lateral accelerationsensor 4 of the vehicle, and a steering wheel angle signal LRW from asteering wheel angle sensor 5 of the vehicle. In block 8 in theanti-tilt control system 2, the tilting limit is estimated from thevehicle mass signal m and an estimated tilting limit signal c1 isoutput.

Furthermore, in block 9 the tilting dynamics are estimated from thesteering wheel angle signal LRW and the vehicle speed signal v; thelocked steering wheel angle and the vehicle speed permit here the changein the lateral acceleration to be estimated and an estimated tiltingdynamics signal c2 to be output. According to this embodiment, theestimation of the tilting dynamics in block 9 does not comprise theinclusion of the lateral acceleration or of the lateral accelerationsignal ay but merely the dynamic change which is to be expected from thesteering wheel angle LRW and the vehicle speed v. In this context, thesteering wheel angle which is determined and the vehicle speed permitsufficiently precise estimation of the expected tilting dynamics inorder to subsequently receive the signals c1 and c2 in a comparisondevice 10 and to compare the tilting limit which is determined orestimated in block 8 with the tilting dynamics estimated in block 9,wherein the lateral acceleration signal ay is advantageouslyadditionally included in this comparison.

The comparison device 10 therefore compares the tilting angles ortilting torques which are expected from the lateral acceleration and thetilting dynamics with the estimated tilting limit, as indicated in FIG.1 by the plus and minus signs, and passes on the anti-tilt comparisonsignal c3, which is generated by the comparison and communicates therisk of tilting or probability of tilting, to an anti-tilt controller 12which subsequently determines the scope of an anti-tilt control processand initiates the latter by outputting a control signal c4 to adeceleration controller 14 for controlling the deceleration by action ofthe brake on one or more axles and/or to a controller 15 for the enginetorque for setting an engine braking effect, which in turn outputcontrol signals S1, S2 to the respective actuating devices. The scope ofthe actuation of the controllers 14 and 15 depends on the necessaryintervention such as, for example, is also known in the case ofactuation of the vehicle brakes or of an engine brake in the case ofbrake control in the longitudinal direction. According to the invention,the deceleration controller 14 can act on one of more brakes of thetraction vehicle and trailer vehicle, preferably it acts on all thebrakes of the traction vehicle and trailer vehicle or trailer.

The yaw control system 3 has a device 16 for determining a yaw setpointvalue which receives the steering wheel angle signal LRW and the vehiclespeed signal v and determines therefrom the yaw setpoint value which isinput by the driver and outputs said yaw setpoint value as a yawsetpoint value signal ψs. During this determination, it is possible inparticular to set travel on a circular path with the steering wheelangle lock and the vehicle speed to which a specific yaw rate isassigned. Furthermore, a device 17 for estimating a yaw actual value,i.e. the actual yaw rate of the vehicle about its vertical axis, isprovided, which device 17 receives the lateral acceleration signal ayand the vehicle speed signal v and outputs a yaw actual value signal ψi.The yaw control system 3 therefore advantageously primarily determinesthe yaw behaviour of the traction vehicle.

The estimation in the device 17 can take place, in particular, byforming a ratio or quotient of the lateral acceleration signal ay andthe vehicle speed signal y, i.e. as ay/v. This is based on the inventiveconcept that during cornering the yaw rate or the yaw actual value ψi ofthe centre of gravity of the traction vehicle is formed by this quotientay/v, and this value can be used in cases in which no lateral skiddingmovement is present, i.e. during desired cornering or even in the caseof understeering. It can therefore be used for control in the case ofundersteering of the traction vehicle; use in the case of an inclinationto oversteer or in the case of oversteering, during which basically askidding movement with a veering-off rear part of the vehicle and frontpart of the vehicle can take place and therefore the yaw rate of thetraction vehicle no longer corresponds to the yaw rate of its centre ofgravity, is therefore detected according to the invention as not beingso advantageous and is not carried out according to this embodiment.

The yaw setpoint value signal ψs and the yaw actual value signal ψi aresubsequently output to a comparison device 18 which compares thesevalues with one another. In this context, it is advantageouslydetermined whether the difference between the setpoint value and theactual value exceeds a predefined threshold value. The comparison device18 outputs a comparison signal c5 to a yaw controller 20 whichsubsequently actuates, with a control signal c6, a controller 21 for theengine torque and/or a controller 22 for brake slip control per sideand/or a brake controller 23 of the trailer, which respectively outputcontrol signals S3, S4, S5 to corresponding actuating devices. AS aresult, the controller is correspondingly actuated for the engine torqueand/or the brake as in the anti-tilt control system 2 above. Basically,the devices 15 and can also be embodied as a common engine torquecontroller which is therefore actuated by the anti-tilt controller 12 oryaw controller 20 depending on the instability which is detected.

The devices 8 to 23 in FIG. 1 are advantageously embodied purely insoftware terms so that implementation as a program in one or moreexisting control devices is possible.

1. Method for controlling the stability of a vehicle, in particular autility vehicle, in which an anti-tilt control method is carried out inwhich at least one lateral acceleration signal (ay), one steering wheelangle signal (LRW) and one vehicle speed signal (v) are received andcontrol signals (S1, S2) for vehicle interventions are formed therefromand output, and a yaw control method is carried out during which thesteering wheel angle signal (LRW), the lateral acceleration signal (ay)and the vehicle speed signal (v) are received, a yaw rate setpoint valuesignal (ψs) and a yaw rate actual value signal (ψi) are determined andcompared with one another, and a yaw control process is carried outduring which control signals (S3, S4, S5) for vehicle interventions areformed and output.
 2. Method according to claim 1, characterized in thatthe yaw rate actual value signal (ψi) is determined, in particularestimated, from at least the lateral acceleration signal (ay) and thevehicle speed signal (v) without using a yaw rate sensor or a yaw ratemeasurement signal.
 3. Method according to claim 2, characterized inthat, in the yaw control method, a yaw rate setpoint value signal (ψs)is determined from the steering wheel angle signal (LRW) and the vehiclespeed signal (v), the yaw rate actual value signal (ψi) is estimatedfrom the lateral acceleration signal (ay) and the vehicle speed signal(v), and the yaw rate setpoint value signal (ψs) and the yaw rate actualvalue signal (ψi) are compared and a yaw controller (20) is actuated asa function of the comparison.
 4. Method according to claim 3,characterized in that the yaw rate actual value signal (ψi) is estimatedfrom a ratio between the lateral acceleration (ay) and the vehicle speed(v).
 5. Method according to claim 3 or 4, characterized in that the yawcontroller (20) actuates a controller (21) for an engine torque and/orat least one brake controller (22, 23).
 6. Method according to claim 5,characterized in that the brake controller (22, 23) is a brake slipcontroller (22), preferably of the rear axle of the traction vehicle,which acts per side of the vehicle, and/or a brake controller (23) of atrailer.
 7. Method according to one of claims 3 to 6, characterized inthat the yaw control method is carried out only when understeering ofthe traction vehicle or an inclination of the traction vehicle toundersteer is detected.
 8. Method according to claim 7, characterized inthat, when understeering of the traction vehicle or an inclination ofthe traction vehicle to understeer is detected, the wheel on a rear axleor on both rear axles which is on the inside of a bend is braked. 9.Method according to one of the preceding claims, characterized in that,in the anti-tilt control method, a vehicle mass signal (m) isadditionally received, a tilting limit of the vehicle is estimated fromthe vehicle mass signal (m), and in a downstream comparison device (10)a tilting state and/or a risk of tilting and/or a probability of tiltingare determined from at least the estimated tilting limit and tiltingdynamics which are estimated from the steering wheel angle signal (LRW)and the vehicle speed signal (v).
 10. Method according to claim 9,characterized in that a reference value of a control system, preferablyof a brake control system (ABS, EBS) is used as a vehicle speed signal(v).
 11. Method according to claim 9 or 10, characterized in that,during the comparison of the estimated tilting limit with the estimatedtilting dynamics, the lateral acceleration signal (ay) is additionallyreceived, and an anti-tilt controller (12) is actuated on the basis ofthe result of the comparison.
 12. Method according to claim 11,characterized in that the anti-tilt controller (12) actuates adeceleration controller (14) for one or more brakes, preferably all thebrakes, of the traction vehicle and of the trailer vehicle.
 13. Methodaccording to claim 11 or 12, characterized in that the anti-tiltcontroller (12) actuates a controller (15) for an engine torque. 14.Device for controlling the stability of a vehicle, which has: ananti-tilt control system (2), which receives at least one lateralacceleration signal (ay) from a lateral acceleration sensor (4), asteering wheel angle signal (LRW) from a steering wheel angle sensor (5)and a vehicle speed signal (v) and forms control signals (S1, S2) forvehicle interventions therefrom and outputs said control signals, and ayaw control system (3) which receives the lateral acceleration signal(ay), the steering wheel angle signal (LRW) and the vehicle speed signal(v), determines a yaw rate setpoint value signal (ψs) and a yaw rateactual value signal (ψi) and compares them with one another, carries outa yaw control process, and outputs control signals (S3, S4, S5) forvehicle interventions.
 15. Device according to claim 14, characterizedin that the yaw control system (3) is embodied without including a yawrate sensor or a yaw rate measurement signal.
 16. Device according toclaim 14 or 15, characterized in that the yaw control system (3) has: adevice (16) for determining a yaw rate setpoint value signal (ψs), whichdevice (16) receives at least the steering wheel angle signal (LRW) andthe vehicle speed signal (v), a device (17) for determining a yaw rateactual value signal (ψi), which device (17) receives at least thelateral acceleration signal (ay) and the vehicle speed signal (v), and acomparison device (18) which receives the yaw rate setpoint value signal(ψs) and the yaw rate actual value signal (ψi) and compares them withone another, and a yaw controller (20) which receives an output signal(c5) of the comparison device (18).
 17. Device according to claim 15 or16, characterized in that the device (17) for determining the yaw rateactual value signal (ψi) estimates the yaw rate actual value signal (ψi)from a ratio between the lateral acceleration (ay) and the vehicle speed(v).
 18. Device according to claim 16 or 17, characterized in that theyaw controller (20) actuates a controller (21) for an engine torqueand/or at least one controller (22, 23) for a braking intervention. 19.Device according to claim 18, characterized in that the yaw controller(20) actuates a controller (22) for brake slip control per side,preferably of the rear axle of the traction vehicle, and/or a brakecontroller (23) of a trailer.
 20. Device according to one of claims 16to 19, characterized in that the yaw control system (3) carries out theyaw control method only when understeering of the traction vehicle or atendency of the traction vehicle to understeer is detected.
 21. Methodaccording to claim 20 and claim 19, characterized in that, whenundersteering or the tendency of the traction vehicle to understeer isdetected, the yaw controller (20) actuates the controller (22) in orderto brake the wheel on the inside of a bend of a rear axle or of bothrear axles.
 22. Device according to one of claims 14 to 21,characterized in that the anti-tilt control system (2) receives avehicle mass signal (m), for example from a further brake control system(ABS, EBS), in particular a brake slip control system.
 23. Deviceaccording to one of claims 14 to 22, characterized in that the anti-tiltcontrol system (2) has: a device (8) for estimating a tilting limit,which device (8) receives a vehicle mass signal (m), a device (9) forestimating tilting dynamics, which device (9) receives the steeringwheel angle signal (LRW) and the vehicle speed signal (v), a comparisondevice (10) for receiving the output signals (c1, c2) of the device (8)for estimating a tilting limit and the device (9) for estimating tiltingdynamics, for receiving the lateral acceleration signal (ay) and foroutputting an anti-tilt comparison signal (c3), an anti-tilt controller(12) for receiving the anti-tilt comparison signal (c3) and actuating adeceleration controller (14) for brakes and/or for actuating acontroller (15) for an engine torque.
 24. Device according to claim 23,characterized in that the deceleration controller (14) is a controllerfor one or more brakes, preferably all the brakes, of the tractionvehicle and of the trailer vehicle.